The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Referring now to FIGS. 1 and 2, a rotating data storage device stores data either magnetically or optically in a rotating medium. For example, rotating storage devices include a hard disk drive (HDD), a compact disc (CD) drive, a digital versatile disc (DVD) drive or a high definition/high data storage disc drive. A HDD system 10 may include read and write channel modules 12, 14 that enable a read/write head or read/write device (both not shown) to write data to a channel/storage medium 16 and to read-back the data. The channel/storage medium 16 may include one or more magnetic disks.
The write channel module 14 may include an encoder module 18 to encode data u(t) and write channel sub-modules 20 to modulate and otherwise prepare the data for storage. Data storage may be affected by internal or external shock, dirt, imperfections on the disk, etc. that may be collectively represented as noise n.
The read channel module 12 may include read channel sub-modules 22 that receive and process read-back data from the channel storage medium 16. The read channel sub-modules 22 may include an analog-to-digital converter (ADC), filters, timing recovery modules, and equalizers. Detector and decoder modules 24 of the read channel module 12 may detect and decode the read-back data.
Referring to FIG. 2, hard disks may include tracks that store data. The tracks are divided into data sectors. Servo numbers may identify servo areas between wedges. A data sector 50 may include a preamble field 52, a sync mark (SM) field 54, a data field 56, and a postamble field 58.
An acquisition preamble is typically recorded in the preamble field 52 to enable the read channel module 12 to acquire the appropriate timing and amplitude information from the read-back signal. The preamble field 52 is also used to lock a clock phase and frequency of a timing loop and to synchronize data that may be in the data field 56. The SM field 54 includes sync-mark data that marks the ending point of the preamble field 52 and the starting point of the data field 56. The SM field 54 may include the same value for all sectors and may be used as a reference point for the position of data throughout the data track. The postamble field 140 is appended to the data sector to help protect the data from detection errors during sector termination.
Due to defects on the media and write/read imperfectness, the read back signal can contain dramatic amplitude fluctuation and cause detection errors or read failures.